A secondary battery supplying driving electric power to a motor of an electric vehicle or the like that is provided for traveling is configured of a plurality of battery modules connected in series, each formed of a plurality of battery cells connected in series. For such a secondary battery, each battery cell's voltage is detected using a technique, for example as disclosed in Japanese Patent Laying-open No. 2005-91062 (Patent Document 1).
Japanese Patent Laying-open No. 2005-91062 discloses an apparatus that detects the voltage of an assembled battery pack, comprising: an assembled battery pack formed of a plurality of unit batteries connected in series; differential amplification units provided for each of the unit batteries to detect the voltage of the unit battery; switch circuits for voltage detection, connecting/disconnecting the unit batteries and the differential amplification units; capacitance adjustment circuits provided for each of the unit batteries and formed of a resistor for discharging and a switch circuit for discharging, connected in series; an A/D conversion unit, and a microcomputer.
As disclosed in Japanese Patent Laying-open No. 2005-91062, when the apparatus that detects the voltage of an assembled battery pack detects each unit battery's voltage, the switch circuits for voltage detection are respectively turned on and all capacitance adjustment circuits are turned off. Thus each differential amplification unit is supplied between each differential input terminal with each unit battery's voltage, and outputs an output voltage corresponding to each voltage. The microcomputer successively takes in the voltage output from each differential amplification unit via the A/D conversion unit to detect each unit battery's voltage.    Patent Document 1: Japanese Patent Laying-open No. 2005-91062